The present invention relates generally to the field of pressurized fluid operated servo mechanisms and, more specifically, to an integral power steering gear assembly for providing a power assist to the manual control of the steering wheels of a vehicle.
Power steering assemblies of the integral type are defined by a single unitary package including an input shaft to control the position of a control valve which controls the flow of pressurized fluid to opposite ends of a piston, which, in turn, controls the position of an output shaft. Additionally, there is a mechanical interconnection between the input shaft and the output shaft which may be utilized or becomes effective upon the loss of hydraulic fluid pressure. These components are in an integral or unitized package which may be attached to a vehicle as a unit with a hydraulic pressure input line and a hydraulic return line connected thereto. The pressure input line communicates with a source of hydraulic pressure, such as a pump, and the return line returns fluid flow to a reservoir, or the like, which stores fluid for use by the pump.
The hydraulic system is closed, however, upon occasion air enters into the system and, depending upon the amount of air, can cause a very dangerous operating situation. For example, too much air in the system can result in a situation where, upon turning the wheels of a vehicle partially in one direction, they could continue to rotate in that direction as air trapped at one end or the other of the piston could be compressed, as compared to the normal situation where hydraulic fluid fills the chambers at either end of the piston to prevent the piston from moving. One of the ways in which air enters into the system is past the shaft seals in the hydraulic pump during cold weather.
One attempt to alleviate the situation is to provide manual bleeds in the system, however, such bleeds are only as effective as the human being relied upon to manually bleed the system and are in no way responsive to the needs of a particular system.